What the ratings mean for fit
The ABB S203MUC-K40 is a 3-pole miniature circuit breaker from the S200MUC series, rated 40 A with a Trip Curve K characteristic. Curve K tolerates motor inrush without nuisance tripping. Rated 277 V AC and 500 V DC, with an interrupting capacity of 6 kA at AC and 10 kA at DC. The DC rating is notably higher than the AC — useful for DC bus or battery-backed circuits where fault currents can be lower but sustained. The 6 kA AC interrupting rating covers standard commercial and light industrial panelboard fault levels; verify it against your available fault current before specifying. Snaps onto standard 35 mm DIN rail — the standard for enclosure mounting in control panels and distribution boards. The 3-pole form factor occupies three modular units of DIN space (each 17.5 mm wide), so factor that into your panel fill.
Panel integration note
Mounts on standard 35 mm DIN rail. The S200MUC series uses a clip-on mechanism — press onto the rail, engage the bottom latch, and it locks in. No tools needed for installation; removal requires a flat-blade screwdriver to release the latch. Wire terminals accept up to 35 mm² conductor for the line and load sides.